Method of protecting crucibles.



FILED STATES PAIEN'I errors,

METHQD or PROTECTING csuolstes.

Specification of Letters Patent.

Patented. Aug. 21, 1906 Application filed August 2,1905. Serial No.'27Z .32 2.

T0 of] 107/ out it mm conc rn.-

Be it known that I, ROBERT A. MCDONALD, a resident of Pittsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Methods of Protectmg ()rucibles; and I do hereby declare the following to be a full, 5

tity of semiliquid clay. Then by rolling the clear, and exact description thereof.

My invention relates to the treating of plumbago or carbon crucibles employed in the manufacture of crucible-steel.

One of the great difficulties to be overcome in the manufacture of crucible-steel is to determine with any degree of accuracy just the amount ofcarbon or silicon which i will be found in the limshed product, owingto i the fact that the molten metal attacks the 1 'walls of the crucible and certain proportions of carbon and silicon are given off and find their way into the steel. possible to make allowance for these additions of carbon or silicon, as the amounts given off vary with each melting operation.

here is no branch of the steel trade that requires greater accuracy in fixing the quantity of carbon, where in the manufacture of high grades of tool-steel the slightest deviation may make the steel entirely unsuitable for the use to which it is to be applied.

The object of my invention is to provide for the treating of the ordinary pluinbago or carbon crucibles so as to prevent the throwing of carbon or silicon and making it possible to obtain with great accuracy just the amount of these constituents which will be obtained in the finished product.

To these ends my invention consistsygenerally stated, in the process of treating ordinary plumbago or carbon crucibles in ap lying. a film of non-carbonaceous materia to the inner walls of the crucible after each heat.

To enable others skilled in the art to practice my invention, I will describe the process in detail.

In carrying out my process I take the ordinary plumbago or carbon crucible as ordinarily employed, and after the charge of moi-- ten metal has been discharged therefrom,

' and preferably while the crucible is slightly warm, I apply to the interiorwalls of the crucible a film of clay. In order that the clay will distribute itself properly over the walls of the crucible, I prefer to prepare it in the following manner: The clay is soaked in water forseveral days and then run through a sieve to takeout any lumps or foreign. mat- T it is of course 1mter and in this semiliquid condition when applied to the'walls of the crucible will flow over the entire. surface, a thin layer or coat ing adhering to the walls of the crucible, while the surplus settles to the bottom. The application of the clay may be made by introducing into the crucible a sufficient quancrucible asufficient quantity adheres to the walls for the purpose of my invention. It is of course apparent that other means may be employed for applying the coating. The crucible is then allowed to dry, when it is in condition to receive another charge of metal, and when said metal has been melted and discharged from the crucible another coating of clay is applied in the same manner above.

I may employ any suitable clay for carrying out my invention; but it must be free from carbonaceous material, which if present would unite with the steel, and so affect the accuracy with which the carbon content is d etermined.

\Vhile I do not wish to limit myself in any way to the composition of the clay further than that it be free from carbonaceous materail, I have found that the following composition gives'very successful results: moisture, 1.80 per cent. water of composition, four per cent; silica, seventy-six per cent; F620,, 4.45 per cent; A1 0 12.75 per cent.

During the melting process a portion of the film applied as above will appear in the form of a flux or slag on the top of the molten steel and forms a covering or protection. against the molten steel taking up oxygen during the period of melting. Practical experience has proven that a. thin coating when applied after each heat will act to prevent the throwing of the carbon, sulfur, and silicon.

Owing to the fact that the crucible does not throw the carbon, sulfur, and silicon, a better and more regular steel can be reduced, for if it is known that the crucib e is not throwing carbon then such additions of carbon-may; be made as necessary, with the result that it is possible to obtain substantially th amount of carbon desired in the finished pro duct.

I am aware that it has been proposed to construct crucibles originally with casings or linings of clay; but these have been ermanent linings formed at the time that t e crucible was made and burned in with the material forming the outer walls of the crucible.

3 eeeeee I do not claim such crucibles formed with 2. The process of treating ordinary plum- 1getrmenen't linings but. my invention is conbagc 'orceibcn ci-ucibles ccnsisting' in epfiily ed to the treating of the crucibles by apin to the inner walls thereof after each eat plying e film of clay c1- cther suitaiile mma in of ciey.

5 carbonaceous material after each heat. In testimony whereof I, the said ROBERT 15 What 'I claim is- A. MODBNALD, have hereunto set'mbrajnd. 1. The process of treatingci'dinei'y plum- @QBERT A. McDO ALD.

hago or carbon crucibles, consisting apply- Witnesses: to'the inner walls thereefeftei' each heat ROBERT 6. 3 00321221,

10 a m-ef-nomccrbonaceous materiel. G. O. RAWOHD. 

